The present invention relates to an expansion valve and to a method for manufacturing the expansion valve conventionally used in a refrigerating cycle of an automobile air-conditioner or the like for adiabatically expanding a high temperature, high-pressure liquid refrigerant to turn the refrigerant into a low temperature low-pressure gas liquid mixture of refrigerant and also for controlling the flow rate of the refrigerant such that the refrigerant has a predetermined degree of overheat at the outlet of an evaporator. The expansion valve according to the invention includes a in-built valve unit, said valve unit having the function of a temperature sensing section detecting the degree of refrigerant overheat at an outlet of an evaporator and the function of a valve element controlling a passing amount of high-pressure refrigerant to be adiabatically expanded in accordance with changes of the degree of refrigerant overheat as detected by said temperature sensing section.
In known refrigerant cycles of car air-conditioners the expansion valve arranged in an evaporator casing is connected to refrigerant inlet and outlet pipes of the evaporator which is arranged in the vehicle compartment. Said expansion valve is also connected to pipes leading to a compressor and a condenser, respectively, both of which are arranged in the engine compartment.
The mounting of a conventional expansion valve is illustrated in FIG. 19. The expansion valve 111 is fixed to a partition wall 112 separating the vehicle compartment from the engine compartment. Due to the irregular external shape of expansion valve 111 a connector 113 is needed as an adapter matching to the external shape of the expansion valve. Connector 113 is joined to that side of the expansion valve to which the pipes are connected leading to the compressor and the condenser. Around connector 113 an insulator 114 is provided sealing the gap between the connector 113 and the partition wall 112 and between the connector 113 and an evaporator casing 115. Pipes 116 and 117 to compressor and the condenser are connected to connector 113 and fixed thereto by a mounting bolt 119 with a plate 118 interposed therebetween. Pipes 120 and 121 leading to an evaporator are fixed to en evaporator side of the expansion valve 111 by a mounting bolt 123 with a blade plate 122 interposed therebetween. Expansion valve 111 includes a valve unit 124 comprising a temperature sensing section measuring the refrigerant temperature at the outlet of the evaporator and a valve element the degree of opening of which is determined by the refrigerant temperature at the outlet of the evaporator. In FIG. 19 valve 124 has its temperature sensing section arranged outside of the refrigerant pipe. There are other types of expansion valve units where the temperature sensing section is arranged inside the refrigerant pipe. In either type, the expansion valve unit used has a low-pressure passage for the refrigerant exiting the evaporator and a high-pressure passage with the valve element inserted therein for restricting the flow of liquid refrigerant and expanding the refrigerant prior to the refrigerant reaching the evaporator. The temperature sensing section is arranged in the low-pressure passage. The valve element is actuated in accordance with the measured temperature.
Among expansion valves having the temperature sensing section received inside its casing, there is a type known in which the valve unit (temperature sensing section and valve element integrally combined) is completely received in a pressure vessel. The pressure vessel used is formed from extruded aluminium material. A chamber or cavity is cut out for receiving the valve unit. Also the high-pressure and low-pressure passages are formed into said pressure vessel. However, seal members are needed in said pressure vessel, and a lid closing the pressure vessel after the valve unit is inserted, such that any gaps between the valve unit and the refrigerant passages and the surrounding are sealed in order to completely seal the pressure vessel. The plurality of seals needs corresponding manufacturing machining or preparation. Due to the complexity of the seals and their number the likelihood of refrigerant leaking to the outside is high.
It is an object of the present invention to create an expansion valve included into a pressure vessel which expansion valve is constituted by a reduced number of parts and does not require seal members to be inserted or manufacturing preparation for the insertion of seal members.
In the expansion valve according to the invention, the pressure vessel completely enclosing the valve unit is formed solely by resin moulding. By said moulding process it is unnecessary to use seal members such as O-rings, which normally constitute a primary cause of refrigerant leakages to the outside. Forming the pressure vessel solely by resin moulding also allows to reduce the number of parts necessary to constitute the expansion valve, because the pressure vessel is constituted by a single resin-moulded article. The expansion valve is completed for operation as soon as the pressure vessel is formed with the valve unit contained therein. Any further assembling steps can be avoided.
The valve unit is surrounded by two half shells which in turn are surrounded by a body block formed by insert moulding and defining said pressure vessel. Since the pressure vessel is formed solely by resin moulding, any further step of assembling the expansion valve can be omitted. Since neither a lid nor any O-rings are required for sealing purposes, the number of parts of the expansion valve can be reduced, thus reducing the manufacturing and assembling costs. Furthermore, no O-rings are used for sealing purposes, so that the refrigerant is prevented from leaking to the outside.
Both half shells are shaped to define therein a gap at a boundary between the high-pressure region and the low-pressure region. By injecting resin into the gap when the body block or pressure vessel is formed by insert moulding a wall sealing structure is formed by injected resin. It is, therefore, unnecessary to provide any separate seal member at the boundary between the high and low pressure regions.
The expansion valve defines by its pressure vessel an elliptic outer form and as such can serve as a connector so that no separate connector is needed when mounting the expansion valve. A flange is formed on the expansion valve adjacent to its surface to which pipes leading to the evaporator are to be mounted. Thus, satisfactory sealing performance can be ensured with ease by simply interposing an insulator between said flange and the partition separating the vehicle compartment from the engine compartment.
Metal collars are fitted in the respective holes through which the mounting bolts are inserted. In this case any stress induced by tightening the mounting bolts is taken up by the metal collars so that the pressure vessel or body block of the expansion valve made of resin is prevented from being fractured by excessively large stress applied thereto.
Particularly serial production of a large number of identical expansion valves of this type can be carried out with reduced costs. The half shells and the valve units are prefabricated components. The half shells do not need precise machining for positioning sealing members. Sub-units thus can be prefabricated by solely inserting the valve between the interconnected half shells. The sub-units can be comfortably stored and transported to the injection or insertion moulding site and can be placed one by one or in series in the respective mould cavities. By injecting the resin the pressure vessel surrounding each sub-unit and simultaneously the internal sealing member structures necessary between the regions of the expansion valve having different pressures are formed. With the termination of the insertion mould process the expansion valves are readily assembled for use. The degree of freedom to design the outer contour of the pressure vessel in view to easy and comfortable mounting of the expansion valve in an evaporator casing and at the separation wall between the engine compartment and the vehicle compartment and finally the mounting of the expansion are simplified to a considerable extent.